Boyce, VA, United States
Boyce, VA, United States

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Wise M.J.,Blandy Experimental Farm | Wise M.J.,Roanoke College | Vu J.V.,University of Virginia | Carr D.E.,Blandy Experimental Farm
International Journal of Plant Sciences | Year: 2011

Although plant breeding systems are evolutionarily labile, a shift from one system to another can involve formidable ecological obstacles. In order for gynodioecy to evolve from hermaphroditism, the carriers of a male-sterility mutation (i.e., females) must overcome two major hurdles: females must attract pollinators without offering pollen as a reward, and they must produce enough seeds to compensate for the loss of reproduction through the paternal route. We investigated the relative performance of female and hermaphroditic plants in a greenhouse study of Mimulus guttatus originating from a largely hermaphroditic population. Females had larger floral displays than did hermaphrodites, with 5% wider corollas and 34% more flowers open at one time. They also produced 22% more flowers over a lifetime and 25% more ovules per ovary than hermaphrodites, giving females 1.53 times more maternal reproductive potential. In a related experiment, bumblebees visited female plants just as frequently as hermaphroditic plants, even though the females offered no pollen reward. Although the relative advantages enjoyed by females may be insufficient to overcome the obstacles for the evolution of stable gynodioecy, they might be strong enough to explain the maintenance of genetic variation for male-sterility alleles often observed in natural populations of M. guttatus. © 2011 by The University of Chicago. All rights reserved.

Wise M.J.,Blandy Experimental Farm | Abrahamson W.G.,Bucknell University | Cole J.A.,Skidmore College
American Journal of Botany | Year: 2010

Herbivores are among the most pervasive selective forces acting on plants, and the number of plant chemicals that presumably evolved for defense against herbivory is immense. In contrast, biologists are only beginning to appreciate the important roles that architectural traits can play in antiherbivore defense. One putative architectural-resistance trait is the nodding stem apex of some goldenrods (Solidago; Asteraceae). Individuals of S. altissima genets that undergo temporary nodding in the late spring (i.e., "candy-cane" ramets) have been shown to be more resistant than individuals of erect-stemmed genets to certain apex-attacking herbivores. We tested the hypothesis that the greater resistance of candy-cane ramets is accomplished by the ramets' "ducking" from the herbivores. In a greenhouse experiment, nodding candy-cane ramets were significantly more resistant to oviposition by the gall-inducing fly Eurosta solidaginis than were ramets of the same genets that had been experimentally straightened. The straightened candy-cane stems were just as susceptible to ovipositions as were ramets of erect-stemmed genets. Thus, ducking indeed appears to confer a resistance advantage to candy-cane genets of S. altissima. © 2010 Botanical Society of America.

Wise M.J.,Blandy Experimental Farm | Cole J.A.,Skidmore College | Carr D.E.,Blandy Experimental Farm
Entomologia Experimentalis et Applicata | Year: 2010

The maintenance of genetic variation for resistance in a plant population that experiences herbivory suggests that resistance entails costs as well as benefits. Ecological costs - which result from indirect effects that a resistance trait has on other members of the host plant's community - constitute a potentially widespread but relatively understudied constraint on the evolution of resistance. Here, we tested the hypothesis that ecological costs may act to constrain the evolution of the recently identified 'stem-ducking' resistance trait in Solidago altissima L. (Asteraceae). Previous studies have shown that, although ducking is effective against some harmful apex-attacking insects, ducking genets are consistently in the minority in S. altissima populations. Potential ecological costs of ducking include increased susceptibility to non-target herbivores and reduction of attack by the third trophic level (i.e., natural enemies of herbivores). In a field study involving more than 2 100 stems, erect stems of S. altissima were galled about 50% more often than ducking stems by the rosette galler Rhopalomyia solidaginis (Loew) (Diptera: Cecidomyiidae). The two other common stem herbivores in this study - the stem-boring moths (Lepidoptera) Dichomeris inserrata (Walsingham) (Gelechiidae) and Oidaematophorus kellicottii (Fish) (Pterophoridae) - were equally abundant on ducking and erect-stemmed plants, suggesting a lack of ecological cost of ducking in terms of susceptibility to other herbivores. Rhopalomyia solidaginis eggs were parasitized by the wasp Platygaster variabilis Ashmead (Hymenoptera: Platygasteridae) at the same rate whether the eggs were laid on ducking or erect stems, suggesting a lack of ecological costs to ducking in terms of reduced attraction of the third trophic level. This study confirmed that ducking is an effective resistance against apex gallers but did not support the hypothesis that ecological costs keep ducking stems in the minority. © 2010 The Authors. Journal compilation © 2010 The Netherlands Entomological Society.

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